Direct answer :
Width of the enlarged photograph = 14 cm
Steps to derive the correct answer :
Length of a small photograph = 6 cm
Width of a small photograph = 4 cm
Length of the photograph when enlarged = 21 cm
Let the width of the photograph when enlarged be x.
Which means :
[tex] = \tt 4 : 6 : : x : 21[/tex]
[tex] =\tt \frac{4}{6} = \frac{x}{21} [/tex]
[tex] =\tt 4 \times 21 = 6 \times x[/tex]
[tex] =\tt 84 = 6x[/tex]
[tex] =\tt x = \frac{84}{6} [/tex]
[tex] =\tt x = 14[/tex]
Thus, the value of x = 14
Therefore, the width of the enlarged photograph = 14 cm
